Inherently tacky pressure sensitive adhesive (PSA) acrylic polymers formed by emulsion polymerization and which contains a polymerized amounts of at least one vinyl ester and at least one diester of a carboxylic acid, are described in U.S. Pat. Nos. 5,129,126, 5,164,444, 5,264,532 and 5,278,227 to Bernard each incorporated herein by reference. The adhesive products have enjoyed immense commercial success as a general purpose acrylic pressure sensitive adhesives.
The water borne pressure-sensitive adhesives exhibit excellent guillotinability and excellent adhesive performance at room temperature and after elevated temperature aging. Multifunctional monomers may be used to provide hydrogen bonding with functional groups such as carboxyl groups and enhance adhesion to polar substrates without affecting peel and tack. Shear performance may be enhanced by metal cross-linking. Metal cross-linking also creates a highly cohesive net work which enhances guillotine performance.
The inclusion of the vinyl esters, such as vinyl acetate and diesters of dicarboxylic acids, such as dioctyl maleate (DOM) create problems in production. Typical residual vinyl ester monomer content has been high, ranging from about 0.5 to about 1 percent by weight of total monomers fed to the reactor for a typical 3000 gallon stirred emulsion polymerization reactor. In addition, reaction rate is slow, requiring a slow feed lasting over a period of about 10 or more hours. It would be ecologically desirable to reduce residual monomer content of the emulsion polymerization reaction and, if possible, to economically reduce the amount of time required for monomer addition.